Add multiline comment support via %%+ and +%%

syntax/vimwiki.vim

@@ -348,6 +348,14 @@ if vimwiki#vars#get_global('valid_html_tags') !=? ''
 
   execute 'syntax match VimwikiComment /'.vimwiki#vars#get_syntaxlocal('rxComment').
         \ '/ contains=@Spell,VimwikiTodo'
+
+  " Only do syntax highlighting for multiline comments if they exist
+  let s:mc_start = vimwiki#vars#get_syntaxlocal('rxMultilineCommentStart')
+  let s:mc_end = vimwiki#vars#get_syntaxlocal('rxMultilineCommentEnd')
+  if !empty(s:mc_start) && !empty(s:mc_end)
+    execute 'syntax region VimwikiMultilineComment start=/'.s:mc_start.
+          \ '/ end=/'.s:mc_end.'/ contains=@NoSpell,VimwikiTodo'
+  endif
 endif
 
 " tags
@@ -425,6 +433,7 @@ hi def link VimwikiSubScriptT VimwikiSubScript
 
 hi def link VimwikiTodo Todo
 hi def link VimwikiComment Comment
+hi def link VimwikiMultilineComment Comment
 
 hi def link VimwikiPlaceholder SpecialKey
 hi def link VimwikiPlaceholderParam String
@@ -487,4 +496,3 @@ call vimwiki#base#nested_syntax('tex',
 
 
 syntax spell toplevel
-

syntax/vimwiki_default.vim

@@ -95,6 +95,8 @@ let s:default_syntax.rxPreEnd = '}}}'
 let s:default_syntax.rxMathStart = '{{\$'
 let s:default_syntax.rxMathEnd = '}}\$'
 
+let s:default_syntax.rxMultilineCommentStart = '%%+'
+let s:default_syntax.rxMultilineCommentEnd = '+%%'
 let s:default_syntax.rxComment = '^\s*%%.*$'
 let s:default_syntax.rxTags = '\%(^\|\s\)\@<=:\%([^:''[:space:]]\+:\)\+\%(\s\|$\)\@='
 

syntax/vimwiki_markdown.vim

@@ -89,6 +89,9 @@ let s:markdown_syntax.rxPreEnd = '\%(`\{3,}\|\~\{3,}\)'
 let s:markdown_syntax.rxMathStart = '\$\$'
 let s:markdown_syntax.rxMathEnd = '\$\$'
 
+" NOTE: There is no multi-line comment syntax for Markdown
+let s:markdown_syntax.rxMultilineCommentStart = ''
+let s:markdown_syntax.rxMultilineCommentEnd = ''
 let s:markdown_syntax.rxComment = '^\s*%%.*$\|<!--[^>]*-->'
 let s:markdown_syntax.rxTags = '\%(^\|\s\)\@<=:\%([^:[:space:]]\+:\)\+\%(\s\|$\)\@='
 

syntax/vimwiki_media.vim

@@ -70,6 +70,9 @@ let s:media_syntax.rxPreEnd = '<\/pre>'
 let s:media_syntax.rxMathStart = '{{\$'
 let s:media_syntax.rxMathEnd = '}}\$'
 
+" NOTE: There is no multi-line comment syntax for MediaWiki
+let s:media_syntax.rxMultilineCommentStart = ''
+let s:media_syntax.rxMultilineCommentEnd = ''
 let s:media_syntax.rxComment = '^\s*%%.*$'
 let s:media_syntax.rxTags = '\%(^\|\s\)\@<=:\%([^:[:space:]]\+:\)\+\%(\s\|$\)\@='